Help!!! An active ingredient to control insects decay in 50% after 12 hours of application. What percent of active ingredient decays after 36...

Hello!

The rule "an active ingredient to control insects decay in 50% after 12 hours of application" probably holds on not only for the first 12 hours of application, but for the next periods too.

So after the first 12 hours 50% decayed and 50% remains. After the second 12-hour period the remaining 50% lose its 50% (a half), so 25% of the original quantity remains. And after the third 12-hour period, which ends the 36-hours period in question, a half of 25% remains, it is 12.5%.

All except this quantity will decay, this is 100%-12.5%=87.5%. This is the answer.